EXERCISE.

166. The student must write out the formulæ of the following compounds :-Bibromide of butylene, bichloride of propylene, bichloride of amylene, bibromide of hexylene, bichloride of butylene.

935. Preparation of these chlorides, iodides, and bromides. -The direct action of chlorine, iodine, or bromine upon olefiant gas, or any other member of the series, gives respectively the bichloride, biniodide, or the bibromide of the member acted upon.

936. Properties. These compounds are attacked by an alcoholic solution of potash. They are resolved by this agent into a chloride, bromide, or iodide of a radical, the general formula of which is C, Han-1 (919), and hydrochloric, hydrobromic, or hydriodic acid. This property distinguishes them from the following compounds belonging to the haloid compounds of the monatomic alcohol radicals of the first class, viz., C, H ̧Cl, Cl; C2 H, Br, Br ; and C, H, I, I; for these latter bodies are not decomposed by an alcoholic solution of potash.

937. If, after these chlorine or bromine compounds have been obtained, we continue to act upon them with a further quantity of chlorine or bromine, we can replace one or more of the equivalents of hydrogen in the radical by its equivalent of chlorine or bromine. In the case of olefiant gas, all the hydrogen has been removed and replaced by chlorine. Example:

938. The first four compounds, when treated with an alcoholic solution of potash, lose the elements of hydrochloric acid, and their formula then becomes,—

939. By the substitution of one atom of chlorine for one atom of hydrogen in the chlorides of the monatomic

alcohol radicals of the first class, we obtain bodies isomeric with the chlorides of these biatomic alcohol radicals. The two groups of bodies are distinguished from each other by their behaviour with an alcoholic solution of potash, as we have just noticed (936); but these monochlorinated chlorides of the monatomic alcohol radicals play the same part as the chlorides of the biatomic radicals. Monochlorinated chloride of ethyl, (C, H, Cl) Cl, for example, becomes transformed, like its isomer, bichloride of ethylene, C, H, Cl,, into diacetate of glycol, by treating it with acetate of silver; it also fixes, like bichloride of ethylene, two molecules of ammonia, a diammonium chloride being formed, in which the C, H, acts as a diatomic radical.

940. Dr. Maxwell Simpson has lately obtained cyanide of ethylene and cyanide of propylene. He prepared them by treating the bromides of these bodies with cyanide of potassium. A mixture of two equivalents of the cyanide, and one of the bromide, together with a considerable quantity of alcohol, was exposed, in well-corked sodawater bottles, to the temperature of a water-bath for sixteen hours. Subsequently the bottles were opened, and the alcohol separated by distillation. When purified, cyanide of ethylene, below the temperature of 37° C., is a crystalline solid of a light brown colour; above that temperature it is a fluid oil. Cyanide of propylene is a liquid at the ordinary temperature of the air. They are converted by potash, as we have already noticed, the one into succinic acid, and the other into pyrotartaric acid.

APPENDIX H.

APPENDIX TO THE GROUP.

941. When aldehyde is acted upon by pentachloride of phosphorus, an oily liquid is formed, which has the following formula, CH, Cl,; it is therefore isomeric with Dutch liquid, but it is distinguished from that body by its lower boiling point (60° C.) and specific gravity, and by its not being decomposed by an alcoholic solution of potash in the cold, and but slowly when heated. The C, H, is therefore supposed to exist in this and other

compounds we shall notice, as a diatomic radical, and it has been called ethylidene. This radical is isomeric, but not identical with ethylene.

942. When the vapour of aldehyde is passed over pentabromide of phosphorus, in a vessel externally cooled, chemical action ensues, and the products formed are bibromide of ethylidene (C, H, Br2), and oxybromide of phosphorus. The ethylidene compound cannot be separated from the phosphorus compound by fractional distillation, because the former compound is decomposed by heat; but the two compounds can be separated by agitating the mixture with lumps of ice, replacing them as they melt. A dense yellow liquid is thus obtained, which is insoluble in water, but is readily decomposed by it, with evolution of hydrobromic acid.

943. Oil of bitter almonds, and other aldehydes, yield also bichlorides of hydrocarbon radicals when treated with pentachloride of phosphorus. The composition and properties of these bodies we have already noticed in Appendix E, and par. 776.

944. Both bromine and iodine act upon allyl, the one forming bibromide of allyl, and the other biniodide of allyl. These bodies have not yet been sufficiently studied.

NEGATIVE OR ACID CHLORIDES.

945. This group embraces (1) The hydrogen compounds of the biatomic radicals analogous to chlorine. (2) The chlorides of the biatomic radicals of the inorganic oxygen acids. (3) The chlorides of the biatomic radicals of the organic oxygen acids.

(1.) THE HYDROGEN COMPOUNDS OF THE BIBASIC RADICALS ANALOGOUS TO CHLORINE.

946. The radical in the ferrocyanides is biatomic; it may therefore be considered as representing the two equivalents of chlorine in the double molecule of hydrochloric acid. The formula of hydroferrocyanic acid, represented on this type, is {H, [Fe(CN).]}, and the general formula for the ferrocyanides M, [Fe(CN),]}. CHLORIDE OF BIATOMIC CYANOGEN.

(CN), Cl,.

(2.) CHLORIDES OF THE BIATOMIC RADICALS OF THE INORGANIC OXYGEN ACIDS.

Chloride of carbonyl, oxychloride of carbon,.

phosgene gas

CO", CI,

Chloride of sulphuryl

SO, CI,

Chloride of chromyl, or chlorochromic acid Cr, O,, Cl2

(3.) CHLORIDES OF THE BIATOMIC RADICALS OF THE ORGANIC OXYGEN ACIDS.

947. Preparation. These chlorides may be obtained by the action of pentachloride of phosphorus upon the corresponding anhydrous acid.

948. "The action of pentachloride of phosphorus on a bibasic acid, is supposed by Gerhardt to consist of two stages; the first being the formation of an anhydrous acid; the second, the conversion of that compound into a chloride. For example:

C. HOO+PCI,. Cl2 = C,H,O,.O+ 2HCl +POCI1;

H2. O

and C, H, O2. O + P Cl2. Cl2 = C1 H ̧ O2. Cl2 + POCI,;

2.

4 4

whereas, in the case of a monobasic acid, the action consists of one stage only.

"This difference is connected by Gerhardt with the fact that a bibasic acid may be supposed to contain water, whereas a monobasic acid cannot (793). According to Williamson, on the contrary, the two stages of the reaction, in the case of a bibasic acid, are precisely similar to one another, and to the single reaction which takes place with monobasic acids. Thus, with sulphuric acid,

SO2

SO2

O2+ PCI,. Cl2 = 0 + HCl + POCI,;
CIS

and HC1O+P Cl2. Cl2 = S O2. Cl2 + HCl + PO Cl,.

The difference in the two views of the reaction is this,that the former supposes the first stage of the action to consist in the formation of an anhydrous acid; the second supposes an intermediate compound-a chlorohydrate of the acid-to be produced. The formation of this chlorohydrate has been shown by Professor Williamson to take place with sulphuric acid. If, however,

one of the two molecules of hydrochloric acid in Gerhardt's first equation be supposed to remain associated with the anhydrous acid, the two views will nearly coincide. In every case, indeed, the reaction consists essentially in the interchange of O and Cl,."

EXERCISES.

167. Write out the formula for the following substances:-Ferrocyanide of potassium, bichloride of succinyl, ferrocyanide of potassium and barium.

168. How many volumes of these chlorides contain two atoms of chlorine?

TREBLE MOLECULE.

H, Cl,.

POSITIVE CHLORIDES.

CHLORIDES OF THE POSITIVE METALS.

949. The ter and sesqui metals, which we have given under the treble molecule of hydrogen (H,. H,), are capable, of course, of forming ter and sesqui chlorides, bromides, &c., thus :

Au" Cl,; Ffe" Cl,

950. The teratomic chlorides, like the biatomic ones, unite with monatomic chlorides, forming double salts. Example:-K Cl, Au” Cl,.

CHLORIDES OF TRIATOMIC RADICALS.

951. We shall here notice the terchlorides of those radicals which are triatomic.

952. Terbromide of allyl, C, H, Br. Obtained by gradually adding three parts of bromine to two parts of iodide of allyl, C, H, I, cooled in a freezing mixture, leaving the liquid to stand until the next day; then washing the liquid separated from crystallized iodine with alkaline, and afterwards with pure water; dehydrating; distilling (whereupon it turns brown, and gives off iodine vapours); again washing and distilling that which has passed over, collecting apart that which distils between 210° and 220°; cooling the purple-red liquid thus obtained